A geodetic survey by shoran trilateration, to approximately second-order accuracy, of the islands of the Canadian Arctic archipelago was completed in 1957. This was the culmination of a programme started in the south-central section of the country in 1949.Shoran (short-range aid to navigation) was developed during World War II as a navigational aid for precise tactical bombing. It consists of two radar transponders at known points on the ground and another radar unit in an aircraft capable of measuring the time required for radio waves to travel from the aircraft to each ground station and to return. These times are converted to distances by an intricate electro-mechanical system and the distances are shown on counters, reading to 0·001 mile. For the military application the distance between transponders was known and the position of the aircraft could be plotted from the mileage-counter distances; for geodetic application the mileage-counter distances are used to measure the distance between the two transponders.